http://xmlgraphics.apache.org/commons/: Apache XML Graphics Commons is a library that consists of several reusable components used by Apache Batik and Apache FOP. Many of these components can easily be used separately outside the domains of SVG and XSL-FO. (Apache Software Foundation) 
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/* $Id: Vertex.java 750418 2009-03-05 11:03:54Z vhennebert $ */

package org.apache.xmlgraphics.util.dijkstra;


Represents a vertex to be used by DijkstraAlgorithm. If you want to represent a city, you can do "public class City implements Vertex". The purpose of this interface is to make sure the Vertex implementation implements the Comparable interface so the sorting order is well-defined even when two vertices have the same penalty/distance from an origin point. Therefore, make sure you implement the compareTo(Object) and
equals(Object) methods.

/**
 * Represents a vertex to be used by {@link DijkstraAlgorithm}. If you want to represent a city,
 * you can do "public class City implements Vertex". The purpose of this interface is to make
 * sure the Vertex implementation implements the Comparable interface so the sorting order is
 * well-defined even when two vertices have the same penalty/distance from an origin point.
 * Therefore, make sure you implement the <code>compareTo(Object)</code> and
 * <code>equals(Object)</code> methods.
 */
public interface Vertex extends Comparable {

}